6.
Features of ventilatory limitation
• The VO2max is reduced relative to
age, sex and height-matched
normal individuals.
• Heart rate rises with exercise but
because ventilatory failure occurs
before the heart is stressed to its
maximum
• At any given work rate:
– minute ventilation is higher than
normal, as the result of increased
dead-space ventilation.

7.
Features of ventilatory limitation
• At peak exercise:
– Minute ventilation is at or just below
their MVV indicating that they have
no ventilatory reserve.
– Instead of the expected decrease in
arterial PCO2 with maximal exercise,
obstructive lung disease patients will
develop a respiratory acidosis
because they cannot ventilate
enough to eliminate the CO2 being
produced in exercising muscles.

8.
Features of ventilatory limitation
• Because ventilatory mechanics limit the person
before the heart reaches its limits, they never
reach a point where the heart cannot meet the
blood flow demands of the exercising muscle 
significant lactic acidosis does not develop and
you cannot identify a ventilatory threshold.
• Oxygen saturation may fall due to areas of low
V/Q inequality.
• These patients stop exercising due to “dyspnea”.

15.
MVV vs. Exercise hyperpnea
• During exercise: End Expiratory Lung Volume (EELV) is reduced
resulting in tidal breathing occurring at a more optimal position of
the pressure volume relationship of the lung and chest wall with
consequent less work of breathing

16.
Limitation of MVV
– MVV is performed at high lung volumes
– Expiratory flows reach maximum at the
highest lung volumes
– Requires large expiratory pleural
pressures to obtain the high flows early in
expiration (often two to three times those
necessary to produce maximal flows)
– Actually it requires lot of work since you
are working at high EILV/TLC = high
elastic load
– Hence MVV cannot be carried out for >15
to 30 s
– Motivationally dependent
– Ventilatory capacity may also vary during
exercise due to
• bronchodilation
• bronchoconstriction

17.
Tidal volumes (VT)
• For low to moderate
workloads
– increase in VT accounts for
most of the rise in
ventilation
– Increased frequency
contributes small amount
• When VT approaches 5060% of VC
– Frequency is major
contributor

18.
VT
• In restrictive disease,
VT may be relatively
fixed. The increase in
ṼE is primarily by
increase RR.

27.
Ventilatory equivalent for CO2
ṼE/VCO2
• In initial portion both ṼE and VCO2
change linearly till anaerobic
threshold
• Once this is reached, both increase
at faster rate as lactic acid is
buffered by HCO3 to produce more
CO2
• Once buffering cannot keep pace
with metabolic acidemia  ṼE
increases out of proportion to VCO2
and the slope goes upwards

28.
Ventilatory equivalent for CO2
ṼE/VCO2
• Rest: 25-30L/L
• High values are a marker
of inefficient ventilation,
which can be due to
– Hyperventilation
– Increased dead space.

36.
What is Expiratory Flow Limitation
• Percent of VT that
meets/exceeds
expiratory boundary
of MFVL

37.
Functional Residual Capacity
• FRC is the lung volume
achieved with a passive
expiration and is an
equilibrium volume
between the chest wall
forces expanding the lungs
and the recoil forces of the
lungs

38.
End-expiratory lung volume
• Dynamically determined (dynamic FRC) based on
expiratory and inspiratory muscle recruitment and
timing.
• Why should you drop your EELV during exercise
– Requires expiratory muscle recruitment : optimize
inspiratory muscle length
– Energy stored (elastic and gravitational energy) in the
chest wall (rib cage, abdomen, and diaphragm) because of
active expiration provides passive recoil at the initiation of
the ensuing inspiration
• If drop in EELV that is too great
– will cause expiratory-flow limitation near EELV due to the
fall in maximal available air flow as lung volume decreases.

41.
End-inspiratory lung volume
• The lung volume at the end of a
tidal inspiratory breath and is
usually expressed as a percent of
the TLC (EILV/TLC) or FVC (if TLC
not available)
• EILV reaches 75 to 90% of TLC in
heavy exercise in normal
subjects.
• As EILV approaches TLC  lung
compliance begins to fall the
inspiratory elastic load
increases.

42.
End-inspiratory lung volume
• A high EILV (>90%) relative
to TLC may also be a marker
of ventilatory constraint
and an index of increased
ventilatory muscle

43.
When ventilatory demand increases
• Subject increases EELV in order to avoid expiratory
flow limitation and to take advantage of the higher
available maximal expiratory airflows
• EILV increases in order to preserve the exercise VT.

50.
Back to MVV
• We talked about limitations of using MVV
• The breathing reserve using the MVV
therefore only provides limited information
and does not provide insight on
– breathing strategy or
– the degree of expiratory or inspiratory flow
constraints.

51.
Ventilatory capacity (VECAP)
• Calculates a theoretical maximal exercise
ventilation based on the maximal available
inspiratory and expiratory airflows over the
range of the tidal exercise breath placed at the
measured EELV
• Hence - independent of “volitional effort “
• But is better than MVV since it takes into
account – breathing pattern & dynamic
changes in airway function

52.
How to measure VECAP
• Exercise Tidal FVL is aligned within
the MFVL according to the measured
EELV.
• The tidal breath is divided into 50
equal volume segments(ΔV)
• Expiratory time (TE) is determined by
dividing each ΔV by the average
maximal expiratory flow (MEF)
within each volume segment
• Total Expiratory time = ΣTE
• Measure inspiratory to total
breathing cycle time  inspiratory
time
• Expiratory + Inspiratory time 
maximal breathing frequency
• Frequency X VT = ventilatory
capacity

53.
VECAP
• In normal subjects:
– Ventilatory capacity decreases with low level of
exercise – due to decrease in EELV
– Then increase as VT increases when it encroaches
inspiratory reserve volume
• No flow limitation exists if tidal expiratory flows
do not meet or exceed the maximal available
flows at any point throughout expiration

58.
Average fitness
• Flow limitation is present near
peak exercise but over <20% of
the tidal breath and only near
EELV.
• EELV falls by approximately 0.7 L
• EILV can increase up to 80% of
the TLC
• Exercise VE = 68% (of MVV)

59.
Healthy aged
• Flow limitation begins to occur at a
lower ventilation than noted in the
younger subjects
• At peak exercise >50% of the tidal breath
meets or exceeds the expiratory
boundary of the MFVL.
• EELV initially decreases but then begins
to increase with these moderate VE
demands
• At peak exercise, EELV is above the
resting FRC
• EILV reaches >90% of TLC,
• Inspiratory flows approach >90% of the
inspiratory flow capacity, indicating little
reserve available to increase VE and
moderate to severe ventilatory
constraint.

60.
Endurance athlete
• The responses are similar to the average
fit adult up to a ventilation of ~ 110 to
120 L/min
• With heavier exercise and the increased
ventilatory demands, expiratory flow
limitation increases to >50% of the VT
• EILV approaches >85% of the TLC
• Inspiratory flow rates with exercise are
closest in proximity to the maximal
available inspiratory flow rates at 75%
of TLC reaching 6.0 L/s and 95% of the
available flow.

61.
Moderate COPD
• EELV may increase even with
light activity due to the early
degree of expiratory flow
limitation
• By peak exercise, flow
limitation is present over the
entirety of expiration
• Inspiratory flows are produced
that nearly overlap the maximal
inspiratory flows achieved
immediately after exercise.
• EILV approaches >95% of TLC.

62.
Interstitial lung disease
•
•
•
Reduced VC and EELV at rest - little room for an exercise-induced decline in EELV
More dependent on an increase in breathing frequency (and flow) to increase
ventilation.
In those patients stopping exercise due to dyspnea
– significant expiratory flow limitation
– high EILV/TLC is present,
•
In patients stopping exercise due to a complaint of leg
– No flow limitation was observed

65.
Obesity
• Breathe at extremely low lung
volumes at rest
• During exercise despite
significant room in the
inspiratory reserve volume
there is substantial expiratory
flow limitation
• Even though there is
ventilatory reserve (VE/MVV),
there is little room to increase
the expiratory flow.
NORMAL